1. Field of the Invention
The present invention relates to an apparatus for controlling with a microcomputer a combustion device having a combustion section such as a gas burner or the like.
2. Description of Related Art
Conventionally, this kind of apparatus for controlling a combustion device detects various abnormal conditions which take place inside the combustion device. When there occurs a system error which takes place inside a control unit inclusive of a central processing unit (CPU) of a microcomputer, or when there occurs an operation error which is judged by an external signal to be inputted into the control unit, such as a flame failure or the like in a state in which a gas burner is expected to be in operation, a safety valve which is interposed in a gas supply pipe to supply the gas burner with gas is forcibly closed, whereby unburned gas is prevented from being discharged out of the gas burner. The occurrence of the abnormal condition is then alarmed by means of a sound and/or a lamp.
This kind of the combustion device is provided with a reset switch. If an operator or a user of the combustion device has removed the cause for the abnormal condition upon checking the combustion device, and if removed the cause for the abnormal condition to have been removed, he operates the reset switch thereby restoring the microcomputer back to the normal control state.
It is true that the microcomputer is restored by the operation of the reset switch. However, when the power is switched on after being once switched off, the power resetting (i.e., resetting through switching on the electric power) is actuated. As a result, the microcomputer will be reset without operating the reset switch. It is to be noted here that, when the power resetting is actuated, a confirmation is not always made as to whether the cause for the abnormal condition has been removed or not. Therefore, there is a disadvantage in that the microcomputer is reset although the cause for the abnormal condition has not been removed.
In view of the above disadvantage, the present invention has an object of providing an apparatus for controlling a combustion device in which the state of stopping the operation of the combustion device is maintained even if the microcomputer is reset through power resetting, unless the reset switch is operated.
In order to attain the above and other objects, the present invention is an apparatus for controlling a combustion device, the combustion device having a microcomputer for detecting various abnormal conditions which occur in the combustion device and for performing a predetermined processing such as stopping an operation of the combustion device when such abnormal conditions have been detected, the apparatus comprising: a reset switch for resetting the microcomputer; a nonvolatile memory, wherein, when a particular abnormal condition among the various abnormal conditions has occurred, a number of occurrence of the particular abnormal condition is stored in said nonvolatile memory, and wherein, when the microcomputer is reset without resort to the reset switch, the operation of the combustion device is held in a suspended state until the reset switch is operated if the number of occurrence, stored in the nonvolatile memory, of the particular abnormal condition is equal to a predetermined number.
In the conventional apparatus for controlling the combustion device, the number of occurrence of abnormal conditions is stored in a random access memory (RAM). Therefore, if the power is switched off, the memory contained inside the RAM disappears. As a result, even if the cause for the abnormal conditions has not been removed or resolved, once the power resetting is actuated, an ordinary combustion control is started again after the power is switched on.
In the present invention, on the other hand, since the number of occurrence of the particular abnormal condition is stored in the nonvolatile memory, the number of occurrence of the particular abnormal condition will not disappear even if the power is switched off. As a result, even if the power resetting is actuated, it can be judged that the cause for the particular abnormal condition has not been resolved, by checking the number of occurrence of the particular abnormal condition inside the nonvolatile memory when the power is switched on. Once the reset switch is operated, it can be assumed that the cause for the particular abnormal condition has been resolved. The number of occurrence of the particular abnormal condition stored in the nonvolatile memory may thus be reset to zero.
The above-described predetermined number may be set to xe2x80x9c1xe2x80x9d so that, whenever the particular abnormal condition occurs, the operation of the combustion device is stopped immediately. However, if the operation of the combustion device is stopped also at the time of wrong detection of an abnormal condition due to noises or the like, the combustion device will have to be stopped frequently. As a result, the reset switch must be operated each time of such a stopping to the trouble of the operator. To avoid such a trouble, it is preferable to set the above-described predetermined number to xe2x80x9c2.xe2x80x9d If it is so arranged that the microcomputer is reset by software at the time of the first occurrence of the above-described particular abnormal condition, the wrong detection can be dealt with by resetting by software. If the combustion device is really abnormal, the detection of abnormal conditions continues. The operation of the combustion device may be stopped only when the particular abnormal condition has been detected for two times or more.
In case abnormal conditions are frequently detected in a rapid succession when the operator of the combustion device has presumably removed the cause for the abnormal conditions, it is considered that the problem lies in the environment in which the combustion device is being used. Therefore, if the number of operation of the reset switch within a given period of time has reached a predetermined upper limit value, it is preferable to temporarily prohibit the resetting of the microcomputer by means of the reset switch. It is thus so arranged that the environment in which the combustion device is being used must then be checked.